The present invention relates to a control apparatus for controlling the displacement of a variable displacement compressor that forms a refrigerant circuit of a vehicle air-conditioning system.
The displacement of a variable displacement compressor is controlled by a control apparatus, which has a control valve. The control valve includes a pressure sensing mechanism and a solenoid for moving a valve body. The pressure sensing mechanism detects the pressure at a pressure monitoring point in a discharge pressure zone of a refrigerant circuit. The pressure sensing mechanism moves the valve body such that the displacement of the compressor is changed to prevent the fluctuations of the pressure. The current supplied to the solenoid is externally controlled to change a target pressure, which is the base for determining the position of the valve body.
When the compressor is started while liquefied refrigerant is lingering in the refrigerant circuit, the compressor compresses the liquefied refrigerant. This increases the pressure in the discharge pressure zone of the refrigerant circuit, or at the pressure monitoring point, abruptly and excessively. Even if the target pressure is maximized by the control valve, the pressure at the pressure monitoring point exceeds the maximized target pressure. The pressure sensing mechanism moves the valve body to prevent the excessive increase of the pressure. Therefore, the compressor cannot increase the displacement promptly after being started while liquefied refrigerant is lingering in the refrigerant circuit. Thus, the liquefied refrigerant in the compressor is not discharged outside promptly. As a result, vibration and noise are generated for a long time by compressing the liquefied refrigerant.
The objective of the present invention is to provide a control apparatus that increases the displacement of a compressor promptly even when the compressor is started while liquefied refrigerant is lingering in a refrigerant circuit.
To achieve the foregoing objective, the present invention provides a control apparatus for controlling the displacement of a variable displacement compressor that forms a refrigerant circuit of an air-conditioning system. The refrigerant circuit includes the compressor, an external circuit, and a discharge pressure zone, which communicates the compressor and the external circuit and is exposed to refrigerant gas that is discharged from the compressor to the external circuit. The control apparatus includes a control valve and a pressure reducing mechanism. The control valve includes a valve body, a pressure sensing mechanism, and a target pressure changing member. The pressure sensing mechanism has a pressure sensing member and detects the pressure at a pressure monitoring point located in the discharge pressure zone in the refrigerant circuit. The pressure sensing mechanism displaces the pressure sensing member in accordance with the fluctuations of the pressure at the pressure monitoring point such that the pressure at the pressure monitoring point is equal to a target pressure, which is a criteria for determining the position of the valve body. The valve body moves accordingly to cancel the fluctuations of the pressure and thus the displacement of the compressor is changed. The target pressure changing member changes the target pressure by controlling the external force applied to the pressure sensing member. The pressure reducing mechanism draws the pressure at the pressure monitoring point to the pressure sensing mechanism. The pressure reducing mechanism is located in a passage that connects the pressure monitoring point and the pressure sensing mechanism. When the pressure at the pressure monitoring point abruptly increases, the pressure reducing mechanism reduces the increase of the pressure that is detected by the pressure sensing mechanism.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.